SNES games, MP3s, watch, rip and burn CDs and DVDs, pause live TV, record shows, weather, RSS feeds, web, and some extra add-ons.
When I first built it the learning curve was pretty steep. More recent versions of MythTV are a snap on Ubuntu. The NVidia drivers can be installed with the click of a button, and the tuner drivers, which once required compiling 3rd party modules, are now included with the distro.
The downside? You need good, supported hardware. And that isn't cheap. My box if built today would run about $2000. Yes, a Tivo is cheaper. But what Tivo has a wireless net connection and a terabyte of RAID 1 storage? A web browser? Can automagically edit out commercials?
A Tivo is a TV recorder. MythTV is a TV recorder, a video storage system, a web portal, a music server and more.